future: clean single-source support for Python 2/3

I thought that this might come in handy for the Classic to Phoenix migration (I haven't used it myself). As I've no idea who here knows anything about it I thought the fail safe approach was to flag it up. Details here http://python-future.org/

···

--
My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language.

Mark Lawrence